The conventional manhole assembly includes a cast iron frame that defines the manhole and rests on a masonry chimney. The open upper end of the manhole frame is enclosed by a cast iron cover. There is a tendency for rainwater or melting snow to flow into the manhole through the corbel joint between the manhole frame and the chimney, as well as through the joint between the frame and the cover. This results in a substantial volume of water entering the sewage system through the manhole, particularly during periods of heavy rain, thereby overtaxing the municipal sewer system. Because of this, there have been attempts to seal the manhole to prevent leakage of water into the sewage system through the manhole.
One manner of preventing leakage into the manhole is disclosed in U.S. Pat. No. 4,305,679, in which a resilient ring is applied to the inner surface of the manhole frame and chimney and sealing bands clamp the ring against the frame and against the chimney on either side of the corbel joint. While sealing systems as disclosed in U.S. Pat. No. 4,305,679 prevent leakage of water into the manhole through the corbel joint, the internal seal does not prevent the entry of foreign material into the corbel joint which can cause possible misalignment of the manhole frame and cover with respect to the street or roadway. There is a tendency for the manhole frame to heave or lift due to frost, causing an enlargement of the corbel joint. Foreign material, such as sand, or other debris can lodge in the corbel joint preventing the frame from properly reseating. Not only does this increase the depth of the joint to promote greater leakage, but can cause improper alignment of the manhole frame and the cover with respect to the road surface.